The purpose of this study is to assess the long-term mental health effects of nuclear incident at Three Mile Island (TMI). Unlike previously studied disasters, the incident threatened to destroy an entire region, and the ultimate outcome remains highly ambiguous. In light of the persistent danger and unusal stress caused by the incident, the psychological well-being of the TMI resident is a major public health concern. The proposed study is an expansion of an existing epidemiological investigation of the mental health of three groups thought to have been particularly affected by the stress of TMI: mothers of preschool children living within 10 miles of the plant; mental health system clients living within 10 miles of the plant; and workers at the nuclear power plant. These groups were interviewed twice, 9 months and 1 year after the event. The proposed study will assess the long-term mental health effects of the incident by reinterviewing these cohorts at the second, third, and fourth anniversaries of the incident. Two comparison groups will be included, similar residents living near another nuclear power facility in Pennsylvania (who participated in the original study), and similar residents living near a non-nuclear electric generating plant. In addition to assessing mental health with standardized instruments, the role of social networks in modifying the impact of stress over time will be investigated. If another catastrophe occurs at TMI during the course of the study, the samples would be reinterviewed as soon as possible.